Thermoplastic stretch wrap films are commonly used to unitize pallet loads of goods during shipment and storage. Optimally, the films should have good stretch performance (high ultimate elongation), low relaxation over time to prevent film sag and loss of goods from the pallet, good cling to hold the film to itself, good optical properties to view the palletized goods through the stretched film (low haze), and good puncture and tear resistance to resist failure on irregularly shaped or sharped-edged loads.
These stretch wrap films are commonly manufactured by blown film and cast film processes. The films are often monolayer films comprising linear low density polyethylene, but can also be coextruded film structures having different layers.
Coextruded multilayer films are also made which have specific film layers to do specific jobs (e.g., one layer provides cling while another provides stretchability). For example, U.S. Pat. No. 5,019,315 (Wilson), incorporated herein by reference, discloses a coextruded stretch film with two outer layers of LLDPE and a core layer of branched high pressure-type low density polyethylene (LDPE). Other additives are said to be included to help impart tack or cling to the film. Conversely, U.S. Pat. No. 4,339,180 (Briggs et al.) and U.S. Pat. No. 4,418,114 (Briggs et al.), both incorporated herein by reference, describe coextruded stretch wrap films having a core layer of LLDPE and a skin layer of LDPE.
Yet another type of cling wrap film is disclosed in U.S. Pat. No. 4,367,256 (Biel), incorporated herein by reference, where a blend of LDPE and a minor amount of LLDPE is used to make the film. Still another type of cling wrap film is disclosed in U.S. Pat. No. 4,518,654 (Eichbauer et al.), incorporated herein by reference, where an A/B stretch wrap film structure has one sided cling. The cling is imparted by using a specific cling additive, such as PIB to one layer of the structure.
While there have been various solutions to specific stretch wrap film problems, films having an overall balance of properties, including superior stretch and load retention, along with good tear resistance, are still desired for commercial viability in the marketplace.